This invention relates to a method for coking coal, in particular coal with a high or varying content of volatile matter, in cokemaking plants with coking chambers using the non-recovery process or the heat-recovery process, and furthermore to a device required to implement this process by a very simple method by preventing the coke oven from being overheated by supplying water steam. The method referred to in this application is independent of the number of coke ovens used, provided the latter form a battery.
For cokemaking, the preheated coking chamber of the coke oven is filled with a coal bed and closed thereafter. The said coal bed may consist of either a bulk coal charge or a compacted, stamped coal charge. Heating the coal causes a volatilization of the volatile matter contained in the coal, i.e. primarily hydrocarbons. The heat further obtained in the coking chamber of non-recovery coke ovens and heat-recovery coke ovens is exclusively generated by combustion of the volatile coal constituents released that volatilize successively by the advancing heating process.
In conformity with prior art technology, combustion is controlled so as to ensure that part of the released gas which is also denoted as crude gas burns off in the coking chamber directly above the coal charge. Combustion air required for this purpose is aspirated through opening ports in the coke oven doors and oven roof. This combustion stage is also denoted as the 1st air stage or primary air stage. Usually the primary air stage does not lead to a complete combustion. Heat liberated during combustion reheats the coal bed, with an ash layer forming on its surface after a short time. This ash layer provides for an exclusion of air, thus preventing a burn-off of the coal bed in the further course of the cokemaking process. Due to heat radiation from above through the developing ash layer, part of the heat liberated during combustion is transferred into the coal charge. Another part of the generated heat is transferred, predominantly by heat conduction through bricked coke oven walls, into the coal bed. A mere heating of the coal bed from the top, applying just a single air stage, however, would lead to uneconomically long coking times.
Therefore, the crude gas which is partially burnt at the primary air stage, is burnt at another stage, thereby supplying heat to the coal bed from the bottom or from the side. There are two technologies particularly known from prior art: U.S. Pat. No. 4,124,450, in conjunction with patents U.S. Pat. No. 4,045,299 and U.S. Pat. No. 3,912,597 of the same inventor, describes how to pass the hot mixture of combustion waste gas and partially burnt crude gas into channels beneath the coking chamber where it can dissipate part of its heat to the brickwork located under the coal bed and transferring this thermal energy by heat conduction to the coal. A post-combustion in a recuperatively operated combustion chamber arranged between the side walls of the coking chamber is executed in the further course of flow. Due to thermal conduction, the heat generated there is laterally transferred via the coke oven walls to the coal bed, thereby reducing the coking time substantially. Such a combustion stage is also denoted as 2nd air stage or secondary air stage.
The other prior art technology supplies the gas partially burnt at the primary stage via channels located in the coke oven walls and also denoted as “downcomers” to the heating flues in the oven sole beneath the coking chamber where sufficient combustion air is continually aspirated to achieve complete combustion. As a result hereof, the coal charge is supplied with heat both directly by heat radiation from the top and indirectly by heat conduction from the bottom, thereby increasing the coking rate and the oven throughput rate substantially.
According to the prior state of the art in technology, the flue gases evolving as a result of a two-stage combustion in the coke oven are subsequently passed through flue gas channels situated outside the coke oven towards the stack and there they can be evacuated into the atmosphere, as provided for in the non-recovery process, or, in case of the heat-recovery process, they can be passed on, for example, to another plant unit to generate steam.
It turned out to be problematic that the release of volatile coal constituents does not proceed uniformly throughout the coking time. At the beginning of cokemaking, a drop in coke oven room temperature is to be recorded. This is caused by the coal charging procedure, because coal is charged at ambient temperature into the warm coke oven chamber. Subsequently it follows a phase of a violent release of gas of high calorific value. This instant supply of heat in the coke oven can be absorbed by the coal and the coke oven construction materials at a limited speed only. Therefore, the temperature in the coke oven chamber rises in the course of the cokemaking process, and if the charging coal blend has a high content of volatile matter, this may lead to exceeding the limit application temperatures of implemented construction materials of the coke oven or flue gas channels and plant units located further downstream. In the further course of coking time, the release of volatile coal constituents becomes increasingly weaker.
According to the prior state of the art in technology, the temperature in a coke oven is only controlled and regulated in the process by controlling and regulating the volumetric flow of primary and secondary air. It bears a drawback in that an effect on the reaction of cokemaking itself is thus taken, because oxygen contained in primary or secondary air acts as a reaction partner and because its over-stoichiometric or under-stoichiometric presence leads to different combustion stages.
To avoid such problems and to assure a most even heat generation and coke quality possible, a coal blend of several individual coal constituents is charged into the coke oven. The coal blend is conventionally adjusted so as to limit the content of volatile matter by a certain maximum value. As a substantial portion of the coal resources available worldwide fails to satisfy this criterion, the availability of coal suitable for this cokemaking process is restricted by this approach, thus leading to economic drawbacks.